#include<stdio.h>
#include<conio.h>
#include<iostream>
using namespace std;
class CPolygon
{
protected:
	int width,height;
public:
	void setValues(int a,int b);
};
void CPolygon::setValues(int a,int b)
{
	width=a;
	height=b;
}
class CTriangle:public CPolygon
{
public:
	int area();
};
int CTriangle::area()
{
	return(width*height/2);
}
int main()
{
	CTriangle trgl;
	trgl.setValues(4,5);
	cout<<trgl.area()<<endl;
	getch();
	return 0;
}